Vertically-oriented, centrifugal, slurry pumps have been used effectively in slurry tanks for quite some time. Both single suction and dual suction pumps have been utilized. A dual suction pump of a conventional submerged type is illustrated in FIG. 1 as a prior art device.
These dual suction pumps, especially of the type illustrated in FIG. 1, are submerged pumps having an elongated vertical shaft which drives a pump impeller by a remote motor located above the slurry. In a typical dual suction submerged pump, no bearings are exposed or located below the slurry level. These vertical pumps have been used to pump slurries resulting from coal pile runoff, floor washdown, lime mud, fly ash, industrial waste transfer, pickling/plating solutions, mill scale, pulp and paper mill liquids, and the like. The cantilever shaft design permits bearings, seals, etc. to be remote from any corrosive or erosive environment.
Recently, submerged pumps in which the motor and the pump are constructed as a compact, submerged unit have been introduced as slurry pumps. Pumps of this type have been used frequently in dredging operations and are illustrated in the following U.S. Pat. Nos. 4,456,424 to Araoka, 4,650,342 to Goodwin, 4,604,035 to Roberts, 3,741,531 to Chaplygin, et al., 3,873,866 to Vaughan.
These patents generally relate to a centrifugal pump with an auger located below a single, downwardly directed pump inlet. The auger may function slightly differently in these various devices. For example, in Araoka the auger is intended to direct liquid away from the pump and agitate solids such as sand located in a river bed. In contrast, the device of Goodwin is structured to force liquid-containing solids axially towards the pump impeller. The Chaplygin patent discloses a device having a canopy which deflects liquid flow downward to then be sucked upwards through the lower inlet of a single inlet pump.
The Vaughan device is one which a chopping blade is placed underneath a single inlet pump to prevent large agglomerates from entering the pump casing.
A disadvantage of auger equipped submersible pumps having a single inlet proximate the auger is that the agitating action of the auger combined with the suction action of the impeller tends to create a somewhat localized effect. For dredging operations in a very large body of water, e.g. a river, in which the whole purpose of the activity is to remove solids from the bottom, such localized action not only may be readily tolerated, but may be actually desired. However, in a vessel containing a slurry, it is usually desired that the slurry particles be substantially uniformly distributed throughout the slurry. Thus, more than mere localized hydraulic flows are desired in a slurry tank. For example, if hydraulic flow is localized in a slurry tank, the slurry particles may not stay in suspension at points remote from the site of the agitation action.
In pumps of the single inlet type which are known in the prior art, a further disadvantage resides in the fact that these pumps generally require submerged seals and bearings.